x86/mpparse: Rename default_find_smp_config()

MPTABLE is no longer the default SMP configuration mechanism.  Rename it to
mpparse_find_mptable() because that's what it does.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240212154639.306287711@linutronix.de